Reactive radical species (e.g., hydroxyl radical and superoxide) are well-suited as antimicrobial agents as their biocidal activity is broad-spectrum, lessening the likelihood of bacterial resistance and improving efficacy against multiple microbial species and strains. Light-activated antimicrobial surfaces, including titanium dioxide films and photosensitizer-modified polymers, represent new strategies for eliciting antibacterial activity by light-induced generation of reactive radicals and singlet oxygen. Medical implants, catheters, and hospital-associated surfaces that are plagued by bacterial contamination may greatly benefit from the associated disinfection/sanitization capabilities of such surfaces.
Nitric oxide (NO) is another radical species with potent broad-spectrum antimicrobial activity as evidenced by its role in the innate immune response to pathogens. The antimicrobial therapeutic utility of exogenous NO delivery via NO donors (i.e., compounds that store and release NO) has been an active area of research. However, the clinical success of NO-based antimicrobial therapies has been hindered due the limited known methods of storing and controllably releasing enhanced payloads of NO. Macromolecular vehicles (e.g., silica nanoparticles, metallic clusters, and dendrimers) and polymers have been functionalized with multiple NO donor moieties to enable larger reservoirs of deliverable NO. The application of these materials as coatings provides localized NO release at a desired interface (e.g., an indwelling medical device) with effective mitigation of bacterial adhesion. Nevertheless, most of these formulations spontaneously liberate NO upon immersion in physiological solution.